A new study has found that low levels of alcohol consumption – 3 to 6 alcoholic drinks per week– could contribute to a small increase in the risk of breast cancer.
Drinking in both earlier and later adult life is also associated with an increased breast cancer risk, according to the study.
Wendy Y. Chen, M.D., M.P.H., of Brigham and Women’s Hospital and Harvard Medical School, Boston, and colleagues examined the association of breast cancer with alcohol consumption during adult life, including quantity, frequency, and age at consumption.
The study included 105,986 women enrolled in the Nurses’ Health Study, who were followed up from 1980 until 2008 with an early adult alcohol assessment and 8 updated alcohol assessments.
The primary outcome the researchers measured was the risk of developing invasive breast cancer.
During the follow-up period, there were 7,690 cases of invasive breast cancer diagnosed among the study participants.
Analyses of data indicated that a low level of alcohol consumption (5.0 to 9.9 grams per day, equivalent to 3-6 glasses of wine per week) was modestly but statistically significantly associated with a 15 percent increased risk of breast cancer.
In addition, women who consumed at least 30 grams of alcohol daily on average (at least 2 drinks per day) had a 51 percent increased risk of breast cancer compared with women who never consumed alcohol.
The researchers also found that when examined separately, alcohol consumption levels at ages 18 to 40 years and after age 40 years were both strongly associated with breast cancer risk.
The authors add that although the exact mechanism for the association between alcohol consumption and breast cancer is not known, one probable explanation may involve alcohol’s effects on circulating estrogen levels.
The study appeared in the November 2 issue of JAMA.